2684. Maximum Number of Moves in a Grid (#190)

Author: remy727

README.md

@@ -502,6 +502,7 @@
 | 2616 | Minimize the Maximum Difference of Pairs | [Ruby](./algorithms/ruby/2616-minimize-the-maximum-difference-of-pairs.rb) | Medium |
 | 2641 | Cousins in Binary Tree II | [Ruby](./algorithms/ruby/2641-cousins-in-binary-tree-ii.rb) | Medium |
 | 2642 | Design Graph With Shortest Path Calculator | [Ruby](./algorithms/ruby/2642-design-graph-with-shortest-path-calculator.rb) | Hard |
+| 2684 | Maximum Number of Moves in a Grid | [Ruby](./algorithms/ruby/2684-maximum-number-of-moves-in-a-grid.rb) | Medium |
 | 2696 | Minimum String Length After Removing Substrings | [Ruby](./algorithms/ruby/2696-minimum-string-length-after-removing-substrings.rb) | Easy |
 | 2697 | Lexicographically Smallest Palindrome | [Ruby](./algorithms/ruby/2697-lexicographically-smallest-palindrome.rb) | Easy |
 | 2706 | Buy Two Chocolates | [Ruby](./algorithms/ruby/2706-buy-two-chocolates.rb) | Easy |

algorithms/ruby/2684-maximum-number-of-moves-in-a-grid.rb

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+# frozen_string_literal: true
+
+# 2684. Maximum Number of Moves in a Grid
+# https://leetcode.com/problems/maximum-number-of-moves-in-a-grid
+# Medium
+
+=begin
+You are given a 0-indexed m x n matrix grid consisting of positive integers.
+You can start at any cell in the first column of the matrix, and traverse the grid in the following way:
+* From a cell (row, col), you can move to any of the cells: (row - 1, col + 1), (row, col + 1) and (row + 1, col + 1) such that the value of the cell you move to, should be strictly bigger than the value of the current cell.
+Return the maximum number of moves that you can perform.
+
+Example 1:
+Input: grid = [[2,4,3,5],[5,4,9,3],[3,4,2,11],[10,9,13,15]]
+Output: 3
+Explanation: We can start at the cell (0, 0) and make the following moves:
+- (0, 0) -> (0, 1).
+- (0, 1) -> (1, 2).
+- (1, 2) -> (2, 3).
+It can be shown that it is the maximum number of moves that can be made.
+
+Example 2:
+Input: grid = [[3,2,4],[2,1,9],[1,1,7]]
+Output: 0
+Explanation: Starting from any cell in the first column we cannot perform any moves.
+
+Constraints:
+* m == grid.length
+* n == grid[i].length
+* 2 <= m, n <= 1000
+* 4 <= m * n <= 105
+* 1 <= grid[i][j] <= 106
+=end
+
+# @param {Integer[][]} grid
+# @return {Integer}
+def max_moves(grid)
+  steps = Array.new(grid[0].size) { |i| [i, []] }.to_h
+  steps[0] = grid.count.times.to_a
+
+  grid[0].size.times.drop(1).each do |col|
+    grid.count.times do |row|
+      steps[col] << row if (steps[col - 1] & [row - 1, row, row + 1]).any? { |r| grid.dig(r, col - 1).to_i < grid.dig(row, col) }
+    end
+    break if steps[col].empty?
+  end
+
+  steps.count { |(_, v)| v.any? } - 1
+end
+
+# **************** #
+#       TEST       #
+# **************** #
+
+require "test/unit"
+class Test_max_moves < Test::Unit::TestCase
+  def test_
+    assert_equal 3, max_moves([[2,4,3,5],[5,4,9,3],[3,4,2,11],[10,9,13,15]])
+    assert_equal 0, max_moves([[3,2,4],[2,1,9],[1,1,7]])
+  end
+end